Phylum Echinoderm "spiney skin"

Gen. Characteristics

- Triploblastic + true coelom

• Pentamerous radial symmetry (adult)

• Bilaterally symmetric (Larval)

- First Deuterostomes

Endoskeleton

- "test" made of interconnecting plates (ossicles)

- porous

Water Vascular System

Hydraulic tube system used for locomotion and feeding

Madreporite

Sieve through which water enters organism

Ring Canal

Central righted water distribution tube

Radial Canal

Extends down each arm

- connects with ring canal

Ampulla

Swollen muscular sacs regulate water flow to tube feet

Tube Feet

- Extend thru pores in ossicles

- often have suction cups

- some are modified pinchers (pedicellaria)

Digestive system

- ventral & central mouth & stomach

- feathery digestive glands down each arm

- can eviscerate stomach : defense + external digestion

Nervous system

Central nerve ring w/ branches down arms

Reproduction

- sex organs in arms

- asexual regeneration

i. Class Crinoidea

Sea lilies

- feathers for passive filter feeding

ii. Class Asteroidea

Sea stars

- oral & aboral sides

iii. Class Ophiuroidea

Brittle stars

- Highly mobile : creep/swim

- tube feet for feeding

- most diverse class

iv. Echinoidea

Urchins + Sand dollars

- 5 tube feet / lack arms

- eat algae

- Urchins are migratory

v. Class Holothuroidea

Sea cucumbers

- lie on sides

- leathery skin & reduced skeleton